1. Field of the Invention
The invention relates to means for holding test tubes in a centrifuge rotor and, more particularly, to means for holding a plurality of small test tubes in a single cylindrical cavity in the rotor.
2. Description of the Prior Art
Centrifuge rotors may be classified according to their means for holding test tubes as either fixed angle rotors or swinging bucket/swinging rack rotors. Fixed angle rotors have bored therein a plurality of uniformly circumferentially spaced cylindrical cavities, each cavity being designed to contain a single test tube. Fixed angle rotors may have the tube cavities bored at various angles with respect to the axis of the rotor, generally ranging from approximately 35.degree. to vertical. Swinging bucket or swinging rack rotors have a plurality of brackets to each of which may be pivotally mounted a test tube bucket or a rack containing one or more test tubes.
Racks and adapters have been developed for swinging bucket and swinging rack rotors which allow a large number of small test tubes to be mounted in a single rack or bucket. Examples are disclosed in U.S. Pat. Nos. 4,032,066 and 4,141,489 issued to Herschel E. Wright and assigned to the same assignee as the present application, and U.S. Pat. No. 4,068,798 issued to Vernon C. Rohde. A given swinging bucket rotor may be adapted to receive test tubes of various sizes and shapes by selecting from an assortment of racks or adapters designed to accommodate the various sizes of test tubes.
However, fixed angle rotors normally are designed to receive only test tubes having substantially the same diameter as the cylindrical cavities bored in that rotor. Although a test tube cavity in a fixed angle rotor may be modified to accept a smaller diameter test tube, no means has been developed heretofore for holding a plurality of small test tubes in a single test tube cavity.
This shortcoming of presently known fixed angle rotors is significant because many modern clinical and research applications involve the use of smaller size samples, and hence smaller test tubes, than had been commonly used in the past. Many existing fixed angle centrifuge rotors are bit enough to accommodate a large number of these smaller test tubes, but have a small number of large test tube cavities instead of a large number of small cavities. Although such a centrifuge rotor could be replaced by one designed to hold a larger number of smaller test tubes, centrifuge rotors are very expensive, and it often would be preferable to adapt an existing rotor to different applications instead of purchasing new rotors.